Earpieces, also referred to as in-ear monitors and canalphones, are commonly used to listen to both recorded and live music. A typical recorded music application would involve plugging the earpiece into a music player such as a CD player, flash or hard drive based MP3 player, home stereo or similar device using the earpiece's headphone jack. Alternately, the earpiece can be wirelessly coupled to the music player. In a typical live music application, an on-stage musician wears the earpiece in order to hear his or her own music during a performance. In this case, the earpiece is either plugged into a wireless belt pack receiver or directly connected to an audio distribution device such as a mixer or a headphone amplifier.
Earpieces are quite small and are normally worn just outside the ear canal. As a result, the acoustic design of the earpiece must lend itself to a very compact design utilizing miniature components. Some earpieces are custom fit (i.e., custom molded) while others use a generic “one-size-fits-all” earpiece.
Although both in-ear monitors and headphones offer the user the ability to hear a source in stereo,.the source being either recorded or live audio material, in-ear monitors offer significant advantages. First, in-ear monitors are so small that they are practically invisible to people that are at any distance from the user, a distinct advantage to a musician who would like to discretely achieve the benefits of headphones on stage (e.g., improved gain-before-feedback, minimization/elimination of room/stage acoustic effects, cleaner mix through the minimization of stage noise, etc.). Second, due to their size, in-ear monitors have little, if any, effect on the mobility of the user (e.g., musician, sports enthusiast, etc.). Third, in-ear monitors can more easily block out ambient sounds than a set of headphones, thus allowing them to operate at lower sound pressure levels than typical headphones in the same environment, thereby helping to protect the user's hearing.
Prior art in-ear monitors and headphones typically use one or more diaphragm-based drivers. Broadly characterized, a diaphragm is a moving-coil speaker with a paper or mylar diaphragm. Since the cost to manufacture diaphragms is relatively low, they are widely used in most common audio products (e.g., ear buds). Unfortunately due to the size of such drivers, earpieces utilizing diaphragm drivers are typically limited to a single diaphragm. As diaphragm-based monitors have significant frequency roll off above 4 kHz, an earpiece with a single diaphragm cannot achieve the desired upper frequency response while still providing an accurate low frequency response.
An alternate to diaphragm drivers are armature drivers, also referred to as balanced armatures. This type of driver uses a magnetically balanced shaft or armature within a small, typically rectangular, enclosure. Due to the inherent cost of armature drivers, however, they are typically only found in hearing aids and high-end in-ear monitors.
A single armature is capable of accurately reproducing low-frequency audio or high-frequency audio, but incapable of providing high-fidelity performance across all frequencies. To overcome this limitation, armature-based earpieces often use two, or even three, armature drivers. Alternately, a combination of armature and diaphragm drivers can be used. In such multiple driver arrangements a crossover network is used to divide the frequency spectrum into multiple regions, i.e., low and high or low, medium, and high. Separate drivers are then used for each region with each driver being optimized for a particular region. Typically the crossover network is a passive network, thus eliminating the necessity for a separate power source, e.g., a battery, for the headset.